Clutches or jewelry clasps are commonly made up with a female member and a complimentary male member. One common form of clutch is what is known as a box clutch which is used for fastening the ends of necklaces together and is of a type exemplified, as for example, in U.S. Pat. No. 2,986,792. There are also a plurality of pin stem clutches utilizing resilient gripping material, as for example, as disclosed in U.S. Pat. No. 3,945,089, and necklace clutches with resilient inserts as seen in U.S. Pat. No. 3,066,501. Where resilient material is used inside of a body to grip a male member, the resilient material is firmly held within the body and is deformed by the male member. The holding power of a device of this nature is therefore dependent solely on the elasticity of the resilient piece.
Accordingly, it is an object of this invention to provide an improved clutch construction which is based on the utilization of male and female members, and a resilient clutch member retained in a cavity in such a way that when withdrawal is attempted, a partial vacuum is created that develops considerable resistance to removal of the male member.
According to this invention the clutch is formed of two parts, one being a tubular shell which is closed at one end so as to form in effect an open cavity in which a resilient tubular clutch member is retained. The resilient tubular clutch is specifically formed in such a way that its outside diameter is less than the inside diameter of the tubular shell cavity; and further, the resilient tubular clutch member has a longitudinal dimension less than the longtudinal dimension of the shell cavity, so that in effect, the tubular clutch is free to slide within the tubular shell and accordingly must be maintained therein by the provision of a lip at the mouth of the open cavity. Cooperating with the tubular shell is a stud which has a diameter larger than the inner diameter of the clutch member and is, of course, adapted to be inserted and withdrawn from the female clutch member. The sizing of the stud is such that the resilient clutch member will expand toward the wall of the shell and will allow the release of displaced air as the stud member is pushed further inwardly. When the stud is attempted to be withdrawn, the resilient clutch member will slide toward the lip at the open mouth of the cavity in the tubular shell and seal against the lip so that in effect, a vacuum is created in the cavity as further withdrawal is attempted. A clutch member therefore does not depend upon the resilience of the material that is used as a clutch member, but by the sealing thereof of the stud into the shell so that as withdrawal is attempted, a vacuum is created.